1. Field of the Invention
The present invention relates generally to scroll compressors which include fixed and orbiting scroll members and, more particularly, to thrust bearing interfaces located between the fixed and orbiting scroll members.
2. Description of the Related Art
A typical scroll compressor comprises two facing scroll members, each having an involute wrap wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other member, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port. The pockets thereby convey and compress a fluid, typically a refrigerant, contained therein.
During compressor operation, the pressure of the compressed refrigerant tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face of the other scroll member. Such leakage reduces the operating efficiency of the compressor and, in extreme cases, may result in the inability of the compressor to operate.
Undesirable leakage at the tip-to-face interface between scroll members can also be caused by a tilting or wobbling motion of the orbiting scroll member. This tilting motion is the result of overturning moments generated by forces acting on the orbiting scroll which are not symmetrical about the axis of the orbiting scroll. More specifically, the drive force imparted by the crankshaft to the drive hub of the orbiting scroll is spaced axially from forces acting on the scroll wrap due to pressure, inertia and friction. The overturning moment acting on the orbiting scroll member tends to cause it to orbit in a slightly tilted condition so that the lower surface of the plate portion of the orbiting scroll is inclined upwardly in the direction of the orbiting motion. Wobbling motion of the orbiting scroll may also result from the interaction between convex mating surfaces, particularly during the initial run-in period of the compressor. For instance, the mating wrap tip surface of one scroll member and face plate of the other scroll member may respectively exhibit convex shapes due to machining variations or pressure and heat distortion during compressor operation. This creates a contact point between the scroll members, about which the orbiting scroll has a tendency to wobble, until the parts wear in. The wobbling perturbation occurs in addition to the tilted orbiting motion described above.
Efforts to counteract the separating force applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakage, have resulted in the development of a variety of axial compliance mechanisms. For example, it is known to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. One approach is to assure close manufacturing tolerances for the component parts and have a thrust bearing interface between the fixed and orbiting scroll members for conveying axial forces between the members.
Typically, the axial compliance forces bias the tips of the scroll compressor wraps against the inner surface of the opposite scroll and/or may bias sliding surfaces on the outer perimeter of the two scroll members into mutual engagement. Frictional forces are created at these areas of contact as the moveable scroll is orbited about the fixed scroll. Excessive frictional forces generated by the axial compliance mechanism can increase the power required to operate the scroll compressor and have an abrasive effect on the engagement surfaces. The abrasive effects created by the axial compliance forces can damage or lead to excessive wearing of the wrap tips and interior surfaces, or faces, of the two scrolls when the axial compliance forces are borne by these surfaces and thereby negatively impact the sealing ability and longevity of the wrap tips.
Some prior art scroll compressors have utilized reinforcing inserts to provide enhanced resistance to wear. For example, it is known to use wear resistant inserts on the face of the scrolls for bearing against the wrap tips, it is also known to use embedded metallic inserts on sliding surfaces disposed radially exterior to the scroll wraps in plastic scroll members to enhance the wear resistance of the plastic scroll members.